Compressors or fluid-compressing devices are used in various fields of industry for various applications involving compression of (process) fluids, especially (process) gases. Known examples of this are turbocompressors in mobile industrial applications such as exhaust-gas turbochargers or jet engines, but also in static industrial applications such as geared turbocompressors for air fractionation.
In the case of such a continuous-operation turbocompressor, the increase in pressure (compression) of the fluid is brought about by a rotary impulse of the fluid from inlet to outlet being increased by a rotating impeller, having radially-extending vanes, of the turbocompressor, by the rotation of the vanes. Here, that is to say in such a compressor stage, the pressure and temperature of the fluid rise while the relative (flow) velocity of the fluid in the impeller drops. In order to achieve maximum pressure increase or compression of the fluid, multiple such compressor stages can be connected in series.
Turbocompressor architectures are divided between centrifugal and axial compressors.
In an axial compressor, the fluid that is to be compressed, for example a process gas, flows through the compressor in a direction parallel to the shaft (axial direction). In a centrifugal compressor, the gas flows axially into the impeller of the compressor stage and is then deflected outward (radially, in the radial direction). Thus, in the case of multi-stage centrifugal compressors, a flow redirection is required downstream of each stage.
A centrifugal compressor of this type is known from http://de.wikipedia.org/wiki/Verdichter (retrieved Oct. 6, 2014).
Combined architectures of axial and centrifugal compressors use their axial stages to draw in large volumetric flows which are compressed to high pressures in the subsequent centrifugal stages.
While single-shaft machines are usually used, in geared compressors the individual compressor stages are grouped around a bull gear, with multiple parallel shafts—which each bear one or two impellers that are accommodated in volute casings—being driven by a large driving gearwheel, a bull gear.
A geared compressor of this type, a geared turbocompressor produced by Siemens under the reference STC-GC, and used for air fractionation, is known from http://www.energy.siemens.comfhq/de/verdichtung-expansion-ventilation/turboverdichter/getriebeturboverdichter/stc-gc.htm (retrieved Oct. 6, 2014).
Another compressor, in this case a single-stage geared centrifugal compressor with open-form, overhung impeller, a geared turbocompressor produced by Siemens under the reference STC-GO, and used to satisfy the requirements of the metallurgic, fossil and chemical industries, is known from http://www.energy.siemens.com/hq/de/verdichtung-expansion-ventilation/turboverdichter/einstufige-verdichter/stc-go.htm (retrieved Oct. 6, 2014).
In times of increasingly flexible processes, requirements in terms of (closed-loop/open-loop control) flexibility and/or in terms of power generally also increase, especially for turbomachines.
To that end, and in order to improve/increase an efficiency and/or control range of the turbomachines, to influence characteristic diagrams of the turbomachines, or indeed in order to control turbomachines at all, it is known to provide such turbomachines with stators such as generally adjustable inlet stators connected upstream of an axial-flow impeller and/or outlet stators connected downstream of an axial-flow impeller.
Stators of this kind have vanes that are generally arranged in a ring shape and may be (angularly) adjustable by means of an (adjustment) mechanism, and that have profiled vane airfoils around which the (process) fluid flows/can flow and which contribute to optimized guiding of the flow through the turbomachine.
An inlet and outlet stator of this type is known for example from DE 10 2012 216 656 A1. The geared turbocompressor STC-GC also has an inlet stator (upstream of its first stage).
An axial compressor having a guide vane of a stator is known from EP 2 241 722 A1, wherein the guide vane has an inflection point in the profile center line or camber line. WO 2005/059313 A2, WO 2009/086959 A1 and EP 1790 830 A1 each show a turbocharger having corresponding guide vanes at the turbine.
For example—in the case of an adjustable inlet stator—such an adjustable inlet stator is thus used to adapt and/or regulate the (process) fluid entering the turbomachine axially (with respect to the impeller axis), or the flow of this fluid with respect to velocity and flow direction before it is incident on the impeller or on the first impeller stage in dependence on a power requirement for the turbomachine, by (angular) adjustment of the vane airfoils or of the vanes of the vane ring of the inlet stator.
However, in particular in the case of large angular adjustments of the vane airfoils or vanes, the fluid flow no longer follows a profile contour of the vanes or vane airfoils, which is associated with flow losses, reduced efficiency and thus also limits on the (power or flexibility) requirements of the turbomachines.
This is also the case for outlet stators of turbomachines, or angular adjustments there.